A detailed study of the indumentum of the leaves of 133 Pelargonium species led to the classification of the trichomes into 11 different types: 6 non-glandular and 5 glandular hair types. The non-glandular hairs are uni- to multicellular and varying in length, shape and wall thickness. Some hairs have a podium at the base. The glandular hairs consist of a uniserial stalk of varying length and unicellular head of varying shape. The distribution of trichomes and indumentum types in the different taxa of Pelargonium is discussed, with reference to its diagnostic value to indicate phylogenetic relationships.